1. Field of the Invention
This invention relates to the field of network address assigning, and, more specifically, to a system, method, and apparatus for enabling Network Address Translation (NAT) of incoming Session Initiation Protocol (SIP) connections based on Dynamic Host Configuration Protocol (DHCP) address assignments.
2. Background of the Invention
Local area networks (LANs) have been used with network devices such as personal computers. A LAN typically has a set number of unique Internet Protocol (IP) addresses for all of the devices on the LAN. More specifically, multiple computers on the LAN may be represented by the same IP address and use the same router(s). In such embodiments, there may be 10 computers, for example, assigned to one router, where the router has its own unique IP address.
In such a LAN, Network Address Translation (NAT) allows a single device, such as a router, to act as an agent between the Internet, or “public network”, and a local, or “private”, network. This means that only a single, unique IP address is required to represent an entire group of computers.
In such an embodiment, a major problem with using NAT is to locate the correct device on the internal network when a packet from the Internet arrives at the router, because all packets received from the Internet are addressed to the router and not to the devices behind the router. Configuring static mappings in the router can, in some cases, solve the problem. For example, the router may be configured to send all World Wide Web (WEB) traffic to a specific PC behind a router, and send all File Transfer Protocol (FTP) traffic to a different specified PC behind the router. However, the problem with this type of static mapping is that it requires specific configuration of the router, which may be expensive for an ISP shipping thousands of routers. Moreover, it is problematic if several PCs are performing the same service (FTP, WEB, etc.).
When a connection is initiated from a device on the internal network to an external device, the access device can always establish the NAT mapping without the use of any additional information. However, when using NAT, connections may only be made from inside a local network to a location outside of the network. A device outside the network cannot connect to a device on the local network without the router being specifically configured to do so. Therefore, the prior art suffers from a serious inefficiency in that a connection cannot be initiated with a device on a LAN by a device outside the LAN without specific configuration of the router at the LAN.